Human chorionic gonadotropin

Human chorionic gonadotropin (hCG) is a glycoprotein hormone that is normally produced in the human body during pregnancy. It is secreted by the syncytiotrophoblast, a component of the fertilized egg after it implants into the uterine wall.

Structure and Function

hCG is a heterodimeric molecule made up of two subunits: alpha (α) and beta (β). The α subunit is nearly identical to the α subunits of other human glycoprotein hormones such as follicle-stimulating hormone (FSH), luteinizing hormone (LH), and thyroid-stimulating hormone (TSH). The β subunit, on the other hand, is unique to hCG, which provides the hormone's specificity.

The primary function of hCG in the early stages of pregnancy is to maintain the corpus luteum, which in turn continues to secrete progesterone. Progesterone helps to keep the endometrium in a thickened and vascularized state, ideal for nurturing a developing embryo. This mechanism prevents the menstruation and rejection of the developing embryo.

Clinical Significance

In the medical field, hCG is frequently utilized as a marker for pregnancy. Over-the-counter pregnancy tests often detect the presence of hCG in urine. A noticeable increase in the levels of hCG can be detected as early as the second week after fertilization, and its detection forms the basis of most pregnancy tests.

In addition, abnormal levels of hCG can indicate certain health conditions. Elevated hCG levels can be associated with multiple pregnancies (twins, triplets, etc.), gestational trophoblastic disease, or non-gestational cancers including testicular cancer and certain types of ovarian cancer. Low levels can be indicative of ectopic pregnancy or potential miscarriage.

hCG is also utilized in fertility treatments, given its role in promoting ovulation and progesterone production. However, the use of hCG as a weight-loss treatment (the 'hCG diet') is controversial and not supported by scientific evidence.

References

• NCBI: Human Chorionic Gonadotropin
• PubMed: The clinical utility of human chorionic gonadotropin in the reproductive field

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